Temporal Climatology and Anomalous Weather Analysis

Weather and climate in our planet are basic environments for human beings and directly rely on a larger environment in our solar system. However, difference between weather and climate is sometimes confusing. We always hear and read some terms like “climate change”, “weather extremes,” and “climatic anomalies” but many cannot clearly tell what they are. Thus, the definition of weather and climate needs to be physically given first. In this chapter, we first have a glance at our environments and their evolutions from the universe to the solar and the Earth systems.

Wind is the directional motion of air particles. The general circulation is a representation of climatic state of wind, which is a linear and delayed response of periodic solar radiation forcing. The timescale of general circulation is from diurnal cycle to seasonal cycle, while its spatial scale ranges from a small peninsula to continent and basin.

Solar radiation is the essential driving of the atmospheric motion. The spatial distribution and temporal evolution of climatic state is also determined by various surface conditions. The zonally averaged climatic state and its longitudinal deviation have a delayed response to the solar radiation for about one month. For the seasonal march of maximum zonally averaged precipitation, the southernmost, transition and northernmost time points are pentads 8, 28 and 44, respectively.

A definition is needed to identify the global monsoon (GM) domain using a monsoon index. Since most previous studies to establish monsoon indices have been limited to specific regions, they have lacked the applicability to universally describe the GM domain. In this chapter, the GM domain is defined by the regions where the difference of two pentad mean precipitation rates exceeds 4 mm day⁻¹, which is also influenced by the low-level prevailing wind reversal associated with the cross-equatorial flow. This definition not only confirms previous results of the classical GM domain from the tropical Africa to Asia–Australia and non-classical monsoon region in the tropical America, but also solves the issue of missing summer monsoon spots. By applying the k-means clustering method on the climatological evolution of global precipitation, the global precipitation domain is divided into 22 major dry–wet alterative regions under six categories. Considering the seasonal influences of the low-level cross-equatorial flow in these major dry–wet alternative regions, the GM is objectively divided into 16 major regions. The Earth’s surface can be roughly divided into two regions, i.e., monsoon and non-monsoon regions, based on whether the region is influenced by monsoon flow and monsoon rainfall. Thus, there are outer edge active zones of the GM. The East Asian monsoon outer edge active zone has been an old topic since AD 688–742 in ancient China, but a summer monsoon dry–wet index series has only been available since AD 950.

The atmosphere, as an important rotating fluid system in the Earth, is often described by two terms: wave and vortex. An example of decomposing atmospheric variables into climatic component and anomaly is demonstrated in this chapter.

Regional persistent rainfalls, one of the high-impact weather extremes in China, can cause mud slides in maintain regions and floods in plains. Tornadoes, which occur frequently in the central United States and eastern China, are also weather extremes during the warm season.

A heat wave is a prolonged period of excessively hot weather, which may be accompanied by high humidity, especially in oceanic climate countries. A cold event (surge) is a weather phenomenon that is distinguished by a cooling of the air. Heat wave and cold surge are two types of surface temperature anomalous events, so we first need to define them and then to find their early signals from the atmosphere to indicate their coverage, intensity, and duration.

Intensity and track of tropical cyclones (TCs) are two basic elements in operational forecasting. Using a novel approach of decomposing hourly total flow into temporal climatic and anomalous flows (and other anomalous variables), this chapter describes the intensity evolution of TCs and the development of a generalized beta-advection model (GBAM) to improve unusual typhoon track predictions within 2–3 days.

The Arctic is warming two to four times faster than the global average and the Arctic sea ice has undergone a substantial long-term decline with superimposed interannual sea ice minimum (SIM) events over the past decade. Eurasian and tropical climatic events frequently occur with severe drought/flood and cold/warm episodes. What are the relationships among anomalous activities of those general circulations and regional surface climatic anomalies? This chapter will reveal their relationships. First, the seasonal, interannual, and interdecadal variabilities of the Arctic and Polar cell strengths are used to explore their connections with the long-term trends and interannual events of Arctic sea ice as well as precipitation and surface air temperature (SAT) in the Northern Hemisphere (NH). Then, regional and persistent anomalous events are also paid particular attention associated with geopotential anomalies of the troposphere and even the stratosphere. As two examples, the anomalous activities of the South Asian High (SAH), the largest circulation system in the boreal summer over upper troposphere, and the western Pacific subtropical high, are investigated using anomaly-based approach.

Since the early 1970s and the early 1980s, the Madden-Julian Oscillation (MJO) in the tropics and some teleconnections in worldwide have respectively become two important topics in climate study. The former is moving low-frequency fluctuations while the latter is standing oscillations. The goal of this chapter is to re-identify the tropical MJO and worldwide teleconnections using anomaly-based analysis method. For examining teleconnections, the rotated empirical orthogonal Function (REOF) is used to analyze the grid maximum height anomalies (MHAs) respectively in the tropics and the two hemispheres. The height anomalies are filtered and applied to represent MJOs, while eastward and westward propagations of tropical oscillations in the three tropical ocean basins are also introduced using the height anomalies.